Effective heat transfer in a liquid cooling system requires a flowing liquid to be in contact with as much surface area as possible of the material that is thermally coupled to extract heat from the cooled device. Fabrication of a reliable and efficient High Surface to Volume Ratio Material (HSVRM) structure is therefore extremely critical for developing an effective micro-heat exchanger. Use of silicon micro-channels is one heat collector structure in liquid cooling systems previously proposed by the assignee of the present invention. For example, see co-pending U.S. patent application Ser. No. 10/643,684, filed on Aug. 18, 2003 and entitled “APPARATUS AND METHOD OF FORMING CHANNELS IN A HEAT-EXCHANGING DEVICE.”
High aspect ratio channels are fabricated by anisotropic etching of silicon, which has found widespread use in micromachining and MEMS. However, silicon has a low thermal conductivity relative to many other materials, and especially relative to true metals. Though methods for fabrication and designs for micro-heat exchangers from higher conductivity materials exist in the prior art, these either use expensive fabrication technologies or prescribe complicated structures without specifying economically feasible fabrication methods.
For example, U.S. Pat. No. 6,415,860 to K. W. Kelly et al. describes the use of LIGA formed micro-channels in a cross-flow micro-heat exchanger. The method described in the Kelley patent, which is hereby incorporated by reference, uses LIGA, a type of High Aspect Ratio Micromachining (HARM) well-known in the prior art. LIGA is multi-step process comprising lithography, electroplating and micromolding which results in HSVRM structure but is costly due to its use of exotic materials and need for synchrotron radiation.
The method of U.S. Pat. No. 5,274,920 to J. A. Matthews describes a process of fabricating a micro-heat exchanger by laminating multiple plates with recessed regions together. This creates a microstructure comprising a plurality of microscopic slots. Though the structure of each plate is thoroughly described, the patent to Matthews, which is hereby incorporated by reference, describes no cost effective, scalable manufacturing method for the plates.
U.S. Pat. No. 6,014,312 to J. Schulz-Harder et al. describes a heat sink constructed by a set of layers each containing openings. The layers are stacked upon one another, creating a flow path. The patent, hereby incorporated by reference, describes polygonal ring structure openings but describes no method of fabrication for the layers.